It usually means that conversation is muted , so you’ll still get the text, but you won’t get alerts or sounds for it. On iPhone, it commonly indicates that “Hide Alerts” is turned on for that chat.

What it does

  • Messages still arrive normally.
  • Notifications from that chat are silenced.
  • The other person usually does not know you muted them.

How to turn it off

  • Open the conversation.
  • Tap the contact or group name at the top.
  • Turn off “Hide Alerts” or tap the bell icon again.

Small caveat

On some iPhone screens, the bell icon can be a tap-to-toggle button, so the slash may show the action you can take rather than the current state.

If you want, I can also explain what the same symbol means on Samsung or Android phones.